Burner control apparatus



8158? JTLBE MOUNTED FLAME DETECTOR BURNER MOTOR Filed June 28, 1957 C. J. BISHOFBERGER BURNER CONTROL APPARATUS July 14, 1959 DETECTOR ELECTRODES '8 BLAST TLBE MOWTED BURNER I I MOTOR 1 LINE INVEN TOR. CARL J. BISHOF BERGER "2 ATTORNEY United States Patent BURNER CONTROL APPARATUS Carl J. Bishofberger, Minneapolis, Minn, assignor to Minneapolis-Honeywell Regulator Company lVfmne= apolis, Minn., a corporation of Delaware Application June 28, 1957, Serial No. 668,654

Claims. (Cl. 158--28) The present invention is concerned with an improved burner control apparatus and more particularly with an intermittent ignition type of burner control apparatus.

Generally speaking, a fuel burner unit comprises a means such as a valve to control the flow of raw fuel to a fire box and of further means such as an ignition transformer to ignite this raw fuel and normally produce a flame within the fire box. A burner control apparatus which is arranged with such a fuel burner unit to control the safe operation of the unit may be of the constant ignition type in which the ignition transformer is maintained continuously energized so long as a fuel valve is open, or the burner control apparatus may be of the intermittent ignition type in which the ignition transformer is de-energized once flame is sensed at the fuel burner unit.

The intermittent ignition burner control apparatus may provide a flame responsive means which deenergizes the ignition transformer substantially immediately upon flame being detected, or the burner control apparatus may be provided with an ignition timer which is arranged to de-energize the ignition transformer a time period after flame is sensed at the fuel burner unit. Still a further type intermittent ignition apparatus provides an ignition timer which de-energizes the ignition transformer a time period after the fuel valve is opened, the flame normally being established during this time period.

In order to provide completely safe operation of the fuel burner unit, it is necessary to provide a start interlock switch controlled by the ignition timer to insure that the fuel burner valve may not be energized unless the ignition timer is in a position such that the ignition transformer can also be energized. Furthermore, an acceptable burner control apparatus must be provided with a safety lockout switch such that in the event there is a flame failure, the safety lockout switch is energized to subsequently cause de-energization of the burner unit fuel valve and thereby'limit the amount of raw fuel which is admitted to the fire box after the flame has failed.

The present invention is concerned with an improved intermittent ignition burner control apparatus having both a safety lockout switch and an ignition timer, in which the safety lockout switch and the ignition timer actuators are connected one to an end terminal and the other to a tap of a main control relay in such a manner that the timing periods of the safety lockout switch and ignition timer remain substantially independent.

It is also desirable that the burner control apparatus be utilized with a heat anticipating type of thermostat. In this type of thermostat an anticipating heater is arranged with the bimetal of the thermostat such that the thermostat current heats the bimetal and anticipates the heat to be supplied from the fuel burner unit. Such a thermostat provides close temperature control of the area to be heated by the fuel burner unit. In such a burner control apparatus, it is necessary that the thermostat current be maintained substantially constant-both during the initial starting of the fuel burner unit and nates a blockof insulating material which is fixed to the ice 2 during the sustained running period of the fuel burner unit.

It is therefore an object of the present invention to provide an improved burner control apparatus for use with a thermostat, wherein the burner is con-trolled by means of a control relay having a tapped winding and wherein the safety lockout switch actuator is connected to the tap of the winding through a switch closed in the absence of combustion and the ignition timer actuator is connected to an end terminal of the winding, the tap of the relay winding being positioned such that the safety switch actuator remains operatively energized and the ignition timer actuator remains operatively de-energized until such time as flame is sensed at the fuel burner unit.

It is a further object of the present invention to provide an improved burner control apparatus having a control relay with tapped winding, a safety lockout switch including an actuator, a timer including an actuator, and flame responsive means including a normally closed switch, the components of the burner control apparatus being arranged such that the control relay is initially energized through a series circuit including a first portion and the tap of the relay winding, the safety lockout switch actuator and the normally closed flame responsive switch, with the timer actuator and the second portion of the relay winding being connected in parallel with the safety lockout switch actuator and the normally closed flame responsive switch, the safety switch actuator remaining operatively energized and the timer actuator remaining operatively de-energized until a flame is sensed at the fuel burner unit to cause the normally closed flame responsive switch to open.

It is a further object of the present invention to provide an improved burner control apparatus having a control relay with a tapped coil, a normally closed safety lockout switch having an actuator, an ignition timer having a normally closed ignition switch, a normally closed start interlock switch and an actuator, and flame responsive means including a normally closed switch and a normally open switch, the components of the burner control apparatus being arranged such that the control relay is initially energized through a series circuit including a first portion and the tap of the relay coil, the safety lockout switch actuator, the normally closed flame responsive switch, the start interlock switch and the safety lockout switch, with the ignition timer actuator and the second portion of the relay coil being connected in parallel with the safety lockout switch actuator and the normally closed flame responsive switch, the safety switch actuator remaining operatively energized and the ignition timer actuator remaining operatively de-energized until a flame is sensed to open the normally closed flame responsive switch and to close the normally open flame responsive switch, the normally open flame responsive switch being connected in parallel with the start interlock switch.

These and other objects of the present invention will become apparent to those skilled in the art upon reference to the following specification, claims, and drawings, of which: I

Figure 1 is a schematic representation of the present invention, and

Figure 2 is a showing of a gun type oil burner having the units of the burner control apparatus of Figure I mounted thereon.

Referring specifically to Figure 2, the reference numeral 10 designates generally a fuel burner unit in the form of a gun type oil burner. The gun type oil burner 10 is provided with a burner motor 11 which controls an oil pump and a fan to supply oil and combustion air to a fuel burner nozzle 12. The reference numeral 13 desigoil pipe 14 leading to the nozzle 12. The insulating member 13 positions a pair of ignition electrodes 15 relative to the oil nozzle 12 such that upon the ignition electrodes 15 being energized by an ignition transformer, not shown, a spark is produced at these electrodes and the oil being emitted from the nozzle 12 is ignited.

The reference numeral 16 designates the first unit of the burner control apparatus, a flame detector, which is mounted within the blast tube of the oil burner and consists of a normally open switch which is sensitive to characteristics of the flame to close the switch on the presence of flame at the nozzle 12. Flame detector 16 may be of the bimetal type which responds to the heat of the flame at nozzle 12 to close a normally open switch.

The flame detector 16 is connected to conductors 17 and 18 and these conductors lead to the second unit of the burner control apparatus, the second unit being designated by the reference numeral 19. The second unit of the burner control apparatus is connected to a source of alternating voltage by means of conductors 2t and 21. As can be seen in Figure 2, the improved burner control apparatus comprises two units 16 and 19 which are mounted integral with the fuel burner unit and form a part thereof.

Referring now to Figure l, the first unit of the burner control apparatus, that is the blast tube mounted flame detector, is designated within the broken lines 16 where as the second unit of the burner control apparatus is designated within the broken lines 19. The ignition transformer, not shown in Figure 2, is shown in Figure l and designated by the reference numeral 22.

As can be seen clearly in both Figures 1 and 2, it is necessary for the purchaser of the combined fuel burner unit and burner control apparatus to merely connect the conductors 20 and 21 to a source of alternating voltage since the flame detector, the burner motor, and the ignition transformer are factory wired.

Referring specifically to the portion of the burner control apparatus within the broken lines 19, the reference numeral 23 designates a transformer having a primary winding 24 connected to the power line conductors 2t) and 21 and having a secondary winding designated by the reference numeral 25.

The secondary winding 25 of transformer 23 supplies electrical Voltage to a network including a control relay 26 having a tapped winding, the tap dividing the winding into a first portion 27 and a second portion 28. As shown schematically in Figure l, the two portions of winding 26 are wound in aiding relationship. That is, as current flows from one portion of the winding into the other portion, the magnetic flux produced in each of the portions is in mutually aiding relationship. This control relay includes an armature designated by the broken line 29, the armature being arranged to control a first and a second normally open switch designated by the reference numerals 30 and 31, respectively.

The reference numeral 32 designates a flame relay having a winding 33, a movable switch blade 34 and stationary contacts 35 and 36. The movable switch blade 34 is shown in the de-energized condition of the flame relay 32 and in this condition switch blade 34 engages contact 36. The switch 34-35 is therefore a normally closed switch. Upon flame relay 32 being energized, switch blade 34 disengages contact as and moves into engagement with contact 35. Switch 34-35 is therefore a normally open switch.

The reference numeral 37 designates a safety lockout switch having an actuating heater 38, a bimetal 39, and a normally closed switch 41'). Safety lockout switch 37 functions such that after a predetermined time period of operative energization of the actuating heater 38, such that bimetal 39 is heated, bimetal 39 moves to the right and thereby allows the normally closed switch 40 to open. Upon subsequent cooling of bimetal 39, the re set button 41 may be manually depressed to once again cause the switch 40 to assume a normally closed condition, as shown in Figure 1.

The reference numeral 42 designates a further timer in the form of an ignition timer having an actuating heater 43, a bimetal 44, and first and second normally closed switches 45 and 46. The schematic showing of timer 42 in Figure 1 provides an insulating member 47 which mounts contacts of the switches 45 and 46 and which is connected to the upper portion of bimetal 44 by means of a member 48. In actual practice, the timer 42 may be provided with means to cause snap action of the switches 45 and 46. However, for purposes of clarity, this feature is omitted from Figure l. The timer 42 operates such that after a time period of operative energization of the actuator 43, during which the bimetal 44 is heated, the bimetal moves to the right causing the normally closed switches 45 and 46 to open. Switch 45 may be called the ignition switch whereas switch 46 may be called the start interlock switch.

The operation of the fuel burner unit 10 shown in Figure 2 is controlled by means of a thermostat indicated by the reference numeral 49 of Figure 1. This thermostat is shown as a heat anticipating type thermostat and includes an anticipating heater 50. In such a thermostat, the closing of its switch signifies a need for operation of the fuel burner unit and the thermostat current which flows through this switch likewise flows through the anticipating heater 50 to thereby heat the bimetal of the thermostat and anticipate the heat to be received from the fuel burner unit 10.

Operation The improved burner control apparatus of Figure 1 is shown in its standby condition wherein thermostat 49 is not calling for operation of the burner unit 141. In this condition, the control relay 26, the flame relay 32, the safety lockout switch heater 37, and the ignition timer heater 43 are all de-energized.

If it is assumed that a call for operation of the fuel burner unit 10 is not indicated by thermostat 49 closing its switch, an initial energizing circuit is completed through the first portion 27 of the control relay 26, to thereby energize this relay. This circuit can be traced from the left hand end terminal of secondary winding 25 through conductors 51 and 52, the first portion 27 of the winding of relay 26, conductor 53, safety switch actuator 38, conductor 54, the normally closed switch 34-36 of flame relay 32, conductors 55 and 56, the normally closed start interlock switch 46 of ignition timer 42, conductors 57 and 58, normally closed safety switch 40, conductor 59, thermostat 49, and conductors 60 and 61 to the right hand terminal of secondary winding 25.

From this above traced circuit it can be seen that the first portion 27 of the winding of relay 26 is energized only if electrical continuity exists in the actuator 38 of safety switch 37, only if the flame relay 32 is in the deenergized position detecting the absence of flame at fuel burner unit 10, and only if the ignition timer 42 is in its de-energized position wherein it is possible to energize the ignition transformer 22, as will be described. Furthermore, it is to be pointed out that control relay 26 is constructed such that the ampere-turns of the first portion of the winding of this relay is suflicient to cause the.

armature 29 and the normally open switches 30 and 31 to move to a closed position.

The closing of switch 30 completes a circuit placing the second portion 28 of the winding of relay 26 in series with the heater 43 of the ignition timer 42. Furthermore, the series connected combination of portion 28 and heater 43 is connected in parallel with safety switch heater 38 and the normally closed switch 34-36 of the flame relay 32. However, the impedance of heater 43 and the voltage present across the second portion 28 of the winding of relay 26 is such that the current flowing in the circuit including thermostat 49 remains in effect substantially unchanged. Furthermore, the safety switch heater 38 remains operatively energized whereas the heater 43 of the ignition timer 42 remains in effect substantially de-energized. In one particular modification, the first portion 27 of the relay winding consisted of 700 turns whereas the second portion of the relay winding consisted of 200 turns. The impedance of the heater 43 was 250 ohms whereas the impedance of the heater 38 was 75 ohms.

In actual practice, it must be realized that the heater 43 of the ignition timer 42 is in fact energized to a certain extent. However, the energy dissipated in this heater in the modification above mentioned, remained at a low value somewhere around A of a watt so long as the normally closed switch 34-36 of the flame responsive relay 32 remained closed. As will be described, upon a flame being detected, the circuit through the safety switch actuator 38 is open and the relay 26 is maintained energized through a circuit including only the heater 43 of the ignition timer 42, thus operatively energizing heater 43.

Energization of relay 26 also causes normally open switch 31 to close. This completes an energizing circuit for both the burner motor 11 and the ignition transformer 22 of the fuel burner unit 10. This can be seen by tracing a circuit from the power line conductor 20 through conductors 62 and 63, burner motor 11, conductor 65, switch 31, and conductors 66 and 67 to the power line conductor 21. The circuit for ignition transformer 22 extends from conductor 62 through conductor 64, ignition transformer 22, conductor 68, ignition switch 45 and conductors 69 and 67 to power line conductor 21.

Referring to Figure 2, a flame is now normally established at the fuel burner nozzle 12 and this flame is sensed by the blast tube mounted flame detector 16. The detector 16 is designated in Figure 1 as a normally open switch and in the presence of flame at the nozzle 12 this switch is closed. Closing of this switch completes an energizing circuit for the flame relay 32. This circuit can be traced from the left hand terminal of secondary Winding 25 through conductors 51 and 70, winding 33 of relay 32, conductors 71 and 17, switch 16, conductors 18 and 72 and conductor 61 to the right hand terminal of secondary winding 25. Energization of flame relay 32 causes the normally closed switch 34-36 to open and also causes the normally open switch 34-35 to close. As above mentioned, the opening of switch 34-36 deenergizes the heater 38 of the safety switch 37, and causes operative energization of heater 43.

The main control relay 26 is now energized through a maintaining circuit which includes the first and second portions 27 and 28 of the relay winding connected in series, it being remembered that these portions are in series aiding relationship in that the magnetic field produced by each portion adds to that produced by the other portion to produce a resultant magnetic field. This circuitry can be traced from the left hand terminal of secondary 25 through conductors 51 and 52, portions 27 and 28, conductor 73, switch 30, conductor 74, heater 43, conductors 75 and 55, switch 34-35, conductors 76 and 58, safety switch 40, conductor 59, thermostat 49, and conductors 60 and 61 to the right hand terminal of secondary winding 25. From this circuit it can be seen that the heater 43 of ignition timer 42 is now operatively energized for the first time and the bimetal 44 begins to effectively heat.

Energization of flame relay 32 causes switch 34-35 to close, as above mentioned. This switch is in parallel with the start interlock switch 46 of the ignition timer 42. Therefore, as the ignition timer 42 continues to operate a point is reached where the ignition switch 45 and the start interlock switch 46 are opened. The opening of ignition switch 45 de-energizes the ignition transformer 22 of the burner control unit 10, operation of this transformer being no longer necessary since a flame is now established at the nozzle 12. Opening of the start interlock switch 46 insures that upon events such as the momentary opening of thermostat 49, or a power failure, the apparatus cannot immediately recycle until the bimetal 44 of ignition timer 42 is cooled to close both switches 45 and 46 and therefore place the ignition transformer 22 in a condition to again ignite the fuel emitted from the burner nozzle '12.

The apparatus is now in a running condition wherein the flame relay 32 is energized in response to the presence of flame at the burner nozzle 12, the control relay 26 is energized through the winding portions 27 and 28 connected in series, the safety switch heater 38 is de-energized, and the ignition timer heater 43 is energized, the switches 45 and 46 being in an open condition.

The burner control apparatus of Figure l operates in this condition until thermostat 49 opens its switch. Upon thermostat 49 opening this switch, the relay 26 is immediately de-energized to thereby open switch 31. Opening of switch 31 de-energizes burner motor 11 and fuel is no longer admitted to the fire box associated with the nozzle 12. Likewise, the heater 43 of ignition timer 42 is de-energized. Upon the absence of flame being sensed by the detector 16, the flame relay 32 is likewise de-energized. The apparatus is now substantially in the condition shown in Figure 1, the exception being that the switches 45 and 46 controlled by the ignition timer 42 are now both in an open condition. Therefore, should there be an immediate call for operation of the burner unit 10 as evidenced by thermostat 49 closing its switch, relay 26 may not be energized since the initial energizing circuit for this relay is open at start interlock switch 46. The thermostat 49 will remain in a position calling for operation of the burner unit 10 until the bimetal 44 of ignition timer 42 is cooled to a condition where the contacts 45 and 46 are closed. Closing of these contacts completes the above traced initial energizing circuit for the first portion 27 of the winding of relay 26 and the operation above described is repeated.

In the event the detector 16 should fail to sense the absence of flame at the nozzle 12, the flame relay 32 is maintained in an energized condition and the normally closed switch 34-36 remains open. Here again, the thermostat 49 can not re-energize the control relay 26 since the initial energizing circuit is open at the switch 34-36 controlled by the flame relay 32.

In the event that a flame is first established at the nozzle 12, as above described, and then there is a subsequent flamc failure, the detector 16 senses such a flame failure and opens its switch to de-energize flame relay 32. De-energization of this flame relay opens the switch 34-35 which is in the maintaining energizing circuit for control relay 26, thereby causing this relay to drop out. When relay 26 drops out the switches 30 and 31 are both opened and the burner motor 11 is de-energized to prevent the supply of fuel to the fire box. The thermostat 49 remains in a closed position since the thermostat continues to indicate the need for operation of the burner unit 18. However, it is necessary for the actuating heater 43 of ignition timer 42 to cool and allow switches 45 and 46 to again be reset to their closed position before recycle can occur. Upon the ignition timer 42 so cooling, the switches 45 and 46 are closed and the above traced initial energizing circuit for the first portion 27 of relay winding of relay 26 is completed to thereby once again cause the switches 30 and 31 to assume their closed condition. If flame is not established at this time, the relay 26 is maintained energized through this initial 'ener gizing circuit for a time period necessary for heater 38 to heat bimetal 39 of safety lockout switch 37 thereby causing the switch 40 to open. The apparatus is now in a safety lockout condition wherein power is not applied to the burner unit 10 and it is necessary that the bimetal 39 cool and then the safety lockout switch 37 be reset by operation of the button 41.

From the above description it can be seen that i have provided an improved burner control apparatus of the intermittent ignition type wherein a safety switch timer and an ignition timer are associated with a main relay having a tapped coil in such a manner that the operation of each of the two timers is independent of the other timer.

Other modifications of the present invention will be apparent to those skilled in the art and it is intended that the scope of the present invention be limited solely by the scope of the appended claims.

I claim as my invention:

1. Burner control apparatus for use with a fuel burner unit having means responsive t the need for operation of the fuel burner unit, comprising; a control relay having a tapped winding and an arma ure including switch means controlled thereby, one end terminal and the tap of said relay winding defining a first portion of the winding and the other end terminal and the tap of the winding defining a second portion of the winding; a safety lockout switch having an electrically energizable actuator and a normally closed switch controlled thereby, a timer having an electrically energizable actuator and a normally closed switch controlled thereby, flame responsive means including means adapted to be positioned to sense the presence of flame at the fuel burner unit and including a first switch which is closed in the absence of flame and a second switch which is closed in the presence of flame, a source of voltage; circuit means adapted to be controlled by the means responsive to the need for operation of the fuel burner unit connecting said first portion of said relay winding, said safety switch actuator, said first flame responsive switch, said timer switch, and said safety switch in a series circuit to said source of voltage to thereby energize said control relay; circuit means controlled by said control relay switch means arranged to energize said fuel burner unit; circuit means connecting said second portion of said relay winding and said timer actuator in series with each other and in parallel with the series connected safety switch actuator and first flame responsive means switch, the relative impedances of said safety switch actuator and said timer actuator and the position of said tap on said relay winding being such that so long as said first ilame responsive means switch is closed said safety switch actuator is operatively energized and said timer actuator is opera tively deenergizct.; and further circuit means connecting said second flame responsive means switch in parallel :ith said timer switch; said flame responsive means being operative upon flame being established at the fuel burner unit to open said lirst flame rcspon ivc is switch and thereby tie-energize said safety switch actuator and operatively energize said timer actuator, and to subsequently cause said timer switch to open, and to thereafter maintain said control relay continuously energized through both said first and second portions of said control relay winding so long as a flame continues to be present at the fuel burner unit.

2. An intermittent ignition burner control apparatus for use with a fuel burner unit having ignition means comprising; a control relay having a tappe winding and an armature with switch means controlled thereby, the tap on said relay winding separating said relay winding into a first and second portion, said first and second portions being wound in flux adding relationship; an ignition timer having an actuator, a start interlock switch, and an ig nition switch controlled thereby; a safety lockout having an actuator and a normally closed safety switch controlled thereby; flame responsive means including a first normally closed switch and second normally open switch, said first and second flame responsive switches being actuated from said normal condition upon flame being established at the fuel burner unit; a source of voltage; circuit means connecting the first and second portions of said relay winding, said ignition timer actu 3 ator, said ignition timer start interlock switch, and said safety switch in a series circuit to said source of voltage; further circuit means connecting said safety lockout actuator and said first flame responsive means switch in series with each other and in parallel with the second portion of said relay winding and said ignition timer actuator, the impedance values of said ignition timer actuator and said safety lock-out actuator and the position of the tap on said relay winding being so related such that so long as the first switch of said flame responsive means remains in said normally closed position, said safety lockout actuator is operatively energized and said ignition timer actuator is operatively de-energized; circuit means connecting said second flame responsive switch in parallel with said ignition timer start interlock switch; and further circuit means controlled by said control relay switch means and by the ignition switch of said ignition timer connected to the fuel burner unit to operatively energize the fuel burner unit and maintain the ignition means of the fuel burner unit energized for a time period following the sensing of flame by said flame responsive means.

3. An intermittent ignition burner control apparatus for use with a fuel burner unit having fuel supply means and ignition means and means responsive to the need for operation of the fuel burner unit, comprising; a relay having a tapped winding, an armature, and a first and second normally open switch controlled thereby, the tap on said relay winding dividing said relay winding into a first and second portion, said first and second portions being wound in adding relationship; an ignition timer having a first and a second normally closed switch and an electrically energizable actuator, a safety lockout switch having an electrically energizable actuator and a normally closed switch, combustion responsive means having means arranged to be positioned at the fuel burner unit and having a first normally closed switch and a second normally open switch; energizing circuit means for said relay including a series connection of the first portion of said relay winding, said safety switch actuator, said normally closed switch of said combustion responsive means, the first normally closed switch of said ignition timer, said normally closed safety switch, and terminals adapted to be connected to the means responsive to the need for operation of the fuel burner unit, said circuit being effective when closed by operation of the means responsive to the need for operation of the fuel burner unit to cause energization of said safety switch actuator and of the first portion of said relay winding to thereby cause operation of said relay armature and closing of said first and second normally opened relay switches; circuit means control ed by the first of said relay switches energizing the fuel burner unit fuel supplying means and energizing the i nition means through the second normally closed switch of said ignition timer; further circuit means controlled by said second relay switch connecting the actuator of said ignition timer and the second portion of said relay winding in parallel with said safety switch actuator and the first switch of said combustion responsive means, the tap on said relay winding being 30 positioned relative to the impedances of said ignition timer actuator and safety switch actuator such that so long as said first combustion responsive means switch remains closed, said safety switch actuator is operatively energized and said ignition timer actuator is operatively de-energized; and further circuit means connecting said second combustion responsive means switch in parallel with said first ignition timer switch, said combustion responsive means functioning upon a flame being detected at the fuel burner unit to open the circuit to said safety switch actuator and thereby operatively energize said ignition timer actuator, said ignition timer functioning after a time period to open said first and second normally closed switches to thereby open said energizing circuit means for said relay and to de-energize the ignition means of the fuel burner unit.

4. Burner control apparatus for use with a fuel burner unit, comprising; a relay having a tapped winding, an armature and a first and second normally open switch controlled thereby; a safety lockout switch having an electrically energizable actuator and a normally closed switch controlled thereby, a timer having an electrically energizable actuator and a normally closed switch control thereby, flame detecting means arranged to be subjected to flame at the fuel burner unit and having a normally closed switch and a normally open switch; circuit means for initially energizing said relay connecting one end terminal and the tap of said relay winding in series with said safety switch actuator, the normally closed switch of said flame detecting means, said timer switch, and said safety switch to thereby energize said relay winding and cause said first and second relay switches to move to a closed position; circuit means controlled by the first relay switch arranged to energize the fuel burner unit; and further circuit means controlled by the second relay switch connecting said timer actuator to the second end terminal of said relay winding and to the junction of said timer switch and the normally closed switch of said flame detecting means, the tap on said relay winding being positioned such that the electrical characteristics of said timer actuator and the portion of the relay winding between said tap and the second end terminal relative to the electrical characteristics of said safety switch actuator serve to maintain said safety switch actuator operatively energized and said timer actuator operatively de-energized until a flame is detected at said fuel burner unit to thereby cause the normally closed switch of said flame detecting means to open and to cause the normally open switch to close, and circuit means connecting said normally open flame detecting switch in parallel with said timer switch.

5. A two-unit intermittent ignition burner control apparatus for use with a fuel burner unit having fuel supplying means, ignition means and a combustion nozzle comprising; a flame sensing unit arranged to be positioned at the nozzle of the fuel burner unit and including a normally open switch which is closed in the presence of flame at the nozzle, a second unit arranged to be mounted on the fuel burner unit at a position remote from said flame sensing unit, said second unit having a flame relay with a winding and a normally open and a norm-ally closed switch, a main relay with a tapped relay winding and first and second normally open switches, an ignition timer including an actuator and a first and second normally closed switch, and a safety lockout switch having an actuator and a normally closed switch; a source of voltage, circuit means controlled by said flame sensing unit connecting said flame relay winding to said source of voltage to thereby energize said flame relay upon a flame being established at the nozzle; circuit means connecting one end terminal of said control relay winding to said source of voltage and connecting the tap of said winding in series with said safety switch actuator, the normally closed switch of said flame relay, the normally closed switch of said ignition timer, and the normally closed safety switch to said source of voltage to thereby energize said control relay winding and said safety switch actuator, a further circuit controlled by the first normally open switch of said control relay connecting the fuel supplying means to said source of voltage and connecting the ignition means to said source of voltage through the second normally closed switch of said ignition timer; further circuit means controlled by the second normally open switch of said control relay connecting the ignition timer actuator from the second end terminal of said control relay winding to the junction of said normally closed flame relay switch and the first normally closed switch of said ignition timer, the tap on said control relay winding being positioned and the impedances of said safety switch actuator and said ignition timer actuator being related such that said safety switch actuator remains operatively energized and said ignition timer actuator remains operatively de-energized so long as said normally closed flame relay switch is closed, and circuit means connecting said normally open flame relay switch in parallel with said first normally closed switch of said ignition timer.

References Cited in the file of this patent UNITED STATES PATENTS 2,385,426 Taylor et a1. Sept. 25, 1945 2,552,973 Judson Mar. 15, 1951 2,743,768 Schell May 1, 1956 

